1. Field of the Invention
The present invention relates generally to press vibration monitoring and more particularly, to a method of generating a press load/speed vibration severity condition indicator for the determination of press/die long-term operating reliability during production operation and to an apparatus utilizing the information generated by the above method in monitoring press vibration severity.
2. Description of the Related Art
The traditional method for calculating the tonnage of a press die is mainly by a means of static load calculation. A given die has a certain material shear length and a stock material with a certain thickness. From this, the tonnage of the die or the force necessary to shear or form the part may be calculated. Traditional press sizing has been based on xe2x80x9cstaticxe2x80x9d die shear loading as calculated using the equation; [Shear Length (in.)] [Thickness (in.)] [S. (lb/in2)]=Shear Load (lb).
This load (plus forming and blanking static loads) has traditionally been considered the only significant load and thus the peak dynamic load of the press. Generally, on shorter stroke machines at speeds below 300 strokes per minute, dynamic effects are not a major influence on die application severity. As press speeds are increased however, there are several other dynamic influences which become present, thereby creating additional press loadings in addition to increases produced by the actual shear loading above the traditional static calculated value. In many cases, these dynamic loads surpass the shear load as the peak dynamic load. In addition to greater effective shear loads, additional impact forces are created as press speed increases, which further contributes to the vibration of the press structure.
It has been found through experimentation, that as the press speed increases there are impact magnifications to static loads as well as several additional loads that occur that are not present at slower press speeds. There are actually several different sources of additional die load parameters that many press operators, production managers, or owners do not necessarily know exist. At higher speeds, even though not exceeding the capacity of the press, the press requires more force to make the part, which in turn creates a different set of more severe vibration conditions.
At higher press speeds, in the press structure, the loads are applied much more quickly, are released more quickly, and in general are producing a much stronger shock wave which is dispersed and dissipated through the press structure. By increasing the speed of the press, the slide velocity at any given point above the bottom dead center position is increased, thereby increasing the impact forces of the punches on the stock material. These impact force increases are related to the square of the velocity. Therefore, press speed is one of several factors increasing vibration in the press. By running the press at higher speeds, more severe vibration is transmitted through the press.
Thus, the above described dynamic effects that occur during press operation increase the loading and overall vibration levels induced in the press structure, all of which increase with an increase in press speed.
Vibration stress magnifications, created by dynamic load increase, can cause many problems to press structures. Cracks can develop over time anywhere within the press structure or its parts if long term dynamic load increases are unknown or go ignored. Broken structural and component parts such as tie rods, crankshafts, crowns, slides and dynamic balancers have been reported, and in all instances the vibration severity has been able to be correlated by field service failure data to develop specific threshold vibration severity levels measured on the press structure during production. At certain definable vibration severity levels, stress magnification levels will be present thus creating increased maintenance severity problems for the press.
The relative life of a press is thus determinable from the accumulative effects of the vibration severity levels experienced over this period of time. A press may withstand high vibration levels without major structural damage if the duration period is relatively short. Also, a press will certainly withstand low vibration levels without structural damage no matter what the duration period.
Accumulative structural damage will occur, however, when a press is run in a magnified stressed condition as a result of medium to high vibration severity levels over a longer duration period whether run continuously or intermittently. The damage will not necessarily be evident in the early stages but will begin to appear over time.
Vibration monitoring systems of the prior art require that a no load response level be determined with periodic no load checking of the relative level at several specific component locations, to try to evaluate the progress of component deterioration.
What is needed in the art is an apparatus which measures the actual application vibration severity levels while in actual production, which allows the press operator, tooling engineer, production manager, or owner to know the long term reliability effects of running the press at any combination of sensed speed and load, by monitoring the actual vibration severity level of the die application via measurement of press RMS velocity by means of an accelerometer, displaying the vibration severity level, and taking action with such result.
Generally, the present invention provides a method and apparatus for the identification of dynamic press load/speed vibration severity condition and for the determination of press/die long-term operating reliability during production operation for presses of a given design.
More specifically, the process of the present invention measures the vibration severity levels of actual die applications, and electronically converts these measurements to identify the zones for press operating reliability generated by the use of an accelerometer sensor. The system reports vibration severity zones during press production operation. The zones thus established relate the press RMS velocity vibration severity level to the potential long-term operating reliability for the particular press as follows:
Zone 1 Extreme Long-Term Reliability;
Zone 2 Very Good Long-Term Reliability;
Zone 3 Reliable (With Caution); and
Zone 4 Not Advisable For Long-Term Reliability.
During actual press production operation, RMS velocity vibration is monitored, processed and displayed. A sensor, which is preferably an accelerometer, is placed on a location of the press. A calibrated electrical circuit converts the press acceleration signal to determine a press velocity signal, a press displacement signal or an RMS velocity measurement within a roll off frequency range of approximately 10 to 100 Hertz.
The present invention advises of the level of vibration severity and long term reliability of metal forming presses for any application, run at any speed with any material and any tooling set up condition. Previous preventive maintenance vibration monitoring only monitors no load changes to a base reference level of specific components, attained through no load reference level analysis. The previous prior art preventive maintenance vibration level measured under no load conditions do not accurately reflect actual production vibration conditions, as does the present vibration severity monitoring system.
Thus, for reliable long-term press production operation, a particular press must be operated within zones of safe load/speed dynamic combinations which will cause acceptable levels of press vibration severity. Each different press design will have certain inherent vibration dissipation characteristics which will allow it to be safely operated with long term reliability within a range of production speeds and dynamic load combinations.
Each singular press may be monitored using an integral console monitor, or a plurality of presses, alternatively, may be monitored using a single portable measurement unit. A press is monitored during production utilizing the following apparatus.
The invention comprises, in one form thereof, a device for monitoring the severity of operation of applications running in a mechanical press comprising at least one signal generator, a signal conditioner operatively connected to the signal generator for calculating a value from the generated signal, and a display operatively connected to said signal conditioner.
The invention comprises, in another form thereof, a device attachable to a mechanical press to measure the overall severity press conditions comprising an accelerometer for measuring press conditions and creating a corresponding signal and a signal processing means for processing the corresponding signal. The signal processing means is connected to the accelerometer to process the corresponding signal including the following possible branch circuits: an acceleration processing means for calculating a press acceleration signal; a velocity processing means for calculating a press velocity signal; and a displacement processing means for calculating a press displacement signal.
A display means is utilized for displaying at least one of the calculated signals with a switch connecting the acceleration, velocity, and displacement processing means together to thereby permit an operator to select one of the calculated signals for input to the display means.
The display means comprises a means for measuring the voltage of the calculated signals and digitally displaying the voltage as representing a press condition. Additionally, the display means may include a plurality of LED""s arranged to illuminate at separate predefined applied voltage ranges whereby an illuminated LED represents a particular range for a signal input to the display means. The range corresponds to a particular vibration severity zone or range. The LED""s illuminate in different colors depending on the predefined applied voltage range.
The invention comprises, in yet another form thereof, a method of monitoring the long-term reliability of a mechanical press comprising the steps of generating a unique press vibration severity/reliability zone chart, monitoring the vibration severity of the press, and outputting the monitored vibration severity and the corresponding vibration severity/reliability zone.
An advantage of the present invention over the prior art is to allow the press owner to instantaneously predict and determine the long term reliability effects being created by any application during its dynamic operation, under various material, speed, setup, or other operating conditions.
Another advantage of the present invention is that it contains signal processing circuitry to monitor positive and negative peak values and convert their signal levels utilizing a unique root means square (RMS) system converter to convert the signal into DC voltages. LED indicators are utilized for use by non technical personnel which are connected to particular voltage levels to indicate the different vibration severity zones as referenced above. The system can measure actual reliability conditions with any set of die setup variables as they are happening in production.
The present invention overcomes many prior art shortcomings by establishing almost instantly the vibration severity condition of the mechanical press and die application combination created by its current operating set up. This data is then used to guide the user in better understanding the risks being created, and thus operating the press more safely and under production conditions which promotes improved press and die longevity. This data can also be used to guide the user to selection of proper new presses for planned future production applications.